Curb feelers for the tail strake

[Anticept]

Student had a tail strike on N566FD recently, it scratched up the tail strake tip and broke a piece away where it struck. Simple repairs that will only take me a few hours to complete.

 

I already talked to Dave and told him what my intentions are, but basically I want to install curb feelers on the tail that point down and back in a V. The idea is to make it very noisy if the tail gets too close to the ground, that there is a chance it will strike.

 

Are there any thoughts or suggestions as to this modification, or alternatives to tail strike early warning systems? Remember that we use two CTs in flight training a lot (averaging 70 hours a month, over 100 hours at peak and 30-40 during winter), so while strikes are unlikely, they still happen and an early warning system would be a great supplement.

[Ed Cesnalis]

A-cept,

 

I think of 30° and 40° as landing flaps and 15° as a take off setting.  With this mindset you will land more slowly and eliminate the risk of tail strikes.  The students will become more proficient.

 

When conditions warrant and 15° is needed a tail strike isn't likely  because you are using the setting for a reason that will have you landing less nose high.  For me 15° is all that is ever needed for conditions. 

[Anticept]

The last tail strike that we had was 300-400 hours ago, so for a flight training op, it's actually pretty damn good. The idea is that this is an extra measure to warn if someone is getting too close, as a training supplement.

[FlyingMonkey]

Don't they make a skid plate for the CTLS that could also be adapted to the CTSW?  I'm pretty sure I read that somewhere...

[Roger Lee]

Andy,

 

They can be adapted. You need to beef up that area a tad in the under fin before the skid gets attached. It isn't just a screw it on install.

 

 

 

Tail strikes come from pulling the stick back too far when you are a little too fast and getting the nose too high. It can be done in zero flaps easier than 15, but does happen and it did for an LS just north of me a couple days ago. he was trying to do a full stall landing.

The plastic skid can be fitted to the SW or older LS's, but it isn't just a screw on install. Even with the skid you can strike the ground to crumple the underfin. This is good for a minor light scrape, but will still damage the underfin with a little heavier strike. I have seen 2-3 crumpled.

 

The best way to prevent a tail strike is to just stay away from what causes them. Pulling the stick back too far and usually in a full stall landing attempt. Fulls stalls can be done no doubt, but if you add a little speed or pull the stick back a little too fast the tail will touch. What is the magic number for speed? It's a little different for each flap setting and individual landing at the time.

There is nothing that says keep the nose off until the bitter end. So long as the mains hit first why care if the nose touches right after they are down. This is how most CT'ers tend to land anyway.

 

p.s.

 

This is not a full stall landing debate so let's not go 37 pages to get to the end. It has to do with landing technique that can get the tail low enough to touch and that means you have the nose too high.

[Anticept]

We're talking about students gentlemen. There are going to be scrapes and bumps as they learn. Yes, I am familiar with the ability to retrofit the tail skids, but as I have discovered, installing those transfers all the impact energy to the bolt holes, whereas not fitting one causes the striking area to take the impact damage instead. The latter is easier and faster to repair, the former is not.

 

I'm installing these curb feelers as an extra precaution on top of proper training. Thanks for the advice on how to land the aircraft, but we've learned already what it takes (we got this plane at ~300 hours, it now has 2,250 hours on it. The other one has logged 600 hours since we got it). I've also learned that when dealing with students, taking extra precautions is a GOOD thing. That's what the feelers are about, an extra precaution, not a substitution for good technique.

 

I don't want to turn away advice on good landing technique, but I would like to make a point: we've got the landing stuff covered. Over a period of 2,850 hours, we've had 4 tail strikes, one of which was actually the result of a poor attitude student whom was promptly asked to leave (was before my time). That's a pretty phenomenal record, considering.

[WmInce]

I know how to measure this, but does anybody know, right off hand, what the pitch attitude is, in degrees, at which point the CTSW and CTLS will encounter the tail fin contacting the ground?

[Ed Cesnalis]

I didn't mean to offend, mostly I was saying that I normally land with full flaps and I endorse that method.  I wasn't advising you, I"m not familiar with what you teach.  I might guess that you teach 15 for normal landings hence the interest in additional warning.

 

I have a flat spot on the bottom of my fin that was the result of an 80kt day when my CT was parked on the ramp, nose into the wind and seat belt around the stick.

[FastEddieB]

Anticept,

 

A Cirrus timeshare company installed skids on the back of their planes:

 

 

I've done thousands of landing in Cirri, and the only time I had a student lightly drag the tail was in one of those planes, and that was practicing a partial-flap landing, which the POH "cautions" against. Neither I nor my students ever dragged the tail when making the full flap landings Cirrus wants, even with the stick back all the way.

 

Looking at the photo, I suspect had the skid not been there the tail would not have touched. Hence, it served as the warning you seek, not as protection, per se.

 

A piece of spring steel could easily be fabricated at any length you like to give warning, though as a bolt-on mod it might need a "blessing" of some sort.

 

Finally, anyone with a line drawing of a CT and a protractor should be able to come up with the "tail strike angle".

 

I did so with a photo of a Cirrus, and the angle in that case is really quite dramatic:

 

 

Appeared to me to be about 15º.

[Tom Baker]

Personally from an instruction standpoint I find the tail strike to be more of an issue when teaching soft field take offs than any style landings. For this I don't think the feelers will help much.

[FastEddieB]

I've had students hit Cessna tails a few times on simulated soft field takeoffs, and I don't doubt I may have a time or two as well.

 

Check most Cessna 150/152 tail tiedown rings and you're very likely to find a flat spot.

 

In fact, I don't think I've ever hit the tail of my Sky Arrow, which does have a skid, and no one else has flown without me in the plane, yet it has wear marks on it.

 

Weird!

 

I did insert a "Coil Spring Booster Block" a while back to give it more "oomph":

 

[Anticept]

Quoting Charlie tango:

>

>"I didn't mean to offend, mostly I was saying that I normally land with full flaps and I endorse that method.  I wasn't advising you, I"m not familiar with what you teach.  I might guess that you teach 15 for normal landings hence the interest in additional warning."

 

 

No offense taken, I'm just trying to keep the subject focused on the feelers. We also teach 30 knot landings as an experience, but at grass fields so that if the tail bumps or drops to the ground, there's no appreciable damage.

 

Personally from an instruction standpoint I find the tail strike to be more of an issue when teaching soft field take offs than any style landings. For this I don't think the feelers will help much.

 

For soft field landings, because of this increased chance of dragging the tail, we use grass fields. I personally experienced a tail tap while flying with a friend who was PIC of my plane at the time. The tail just bounced off and had a little green skidmark from the grass, but no damage occurred. In fact, I felt the tail bump, but he didn't even realize it, it was that soft and quiet. I'm not worried about tail bumps on soft fields.

 

Looking at the photo, I suspect had the skid not been there the tail would not have touched. Hence, it served as the warning you seek, not as protection, per se.

 

A piece of spring steel could easily be fabricated at any length you like to give warning, though as a bolt-on mod it might need a "blessing" of some sort.

 

That's exactly the purpose, warning, not protection. Thanks for the idea for spring steel, I wasn't sure yet how I was going to do this. I bet I could put a chattering device on it too so that as it drags, it amplifies the noise even in grass.

 

As for the modification, that's why I contacted Dave at FDUSA. This actually caught his attention, he's very interested in what I come up with.

[Ed Cesnalis]

...We also teach 30 knot landings as an experience, but at grass fields so that if the tail bumps or drops to the ground, there's no appreciable damage...

 

 

Interesting,  I have the opinion that it is close to impossible to strike the tail ( on even ground ) in my CTSW landing at 30°.

[Anticept]

CTSW has a shorter tail. Mine is a CTLS, and the extra 18 inches (?) means it is quite a bit more likely.

[FastEddieB]

We're off topic a bit, but the way tail strikes typically happen is the plane gains altitude in a balloon, comes back down and then the student or pilot jerks back on the stick at the last second, rotating the tail into the ground.

 

Had a student do that in my Citabria. Though a tailwheel, it jammed the tailwheel up into the rudder, bending the channel.

 

To be honest, I recall it happening at least twice.

 

Most planes are configured so that if leveled off just over the ground, the pilot will run out of elevator authority well before the tail hits the ground.

 

Though a bit hard to see, this is a screenshot of a full flap, full stall landing in a Cirrus:

 

 

You can probably make out there's still lots of tail clearance.

 

Might be fun to get some shots of CT's landing in a full flap/full stall configuration to see how much clearance there really is.

 

I volunteer as photographer!

[Ed Cesnalis]

...I volunteer as photographer!

 

 

Meet me at my hangar in the morning.

[FastEddieB]

Deal!

 

Just have to find a wormhole on this end!

[FastEddieB]

Anyway, this is very close to a full flap, full stall landing in my Sky Arrow:

 

 

By full stall, I mean the stick is all the way back or nearly so. I think you can see that in the elevator position.

 

Lots of tail clearance. As I said, the only way to strike the tail would be to rotate it into the ground.

 

Now surely someone has some photos or screenshots of CT's doing the same for comparison.

[Doug G.]

Charlie Tango, it sounds like a good idea, but have you given thought to your students reaction to hearing the noise from the feelers? My first instinct as a student would have been to push the stick forward - not good! Will they be trained to always do a go around?

[FastEddieB]

Charlie Tango, it sounds like a good idea, but have you given thought to your students reaction to hearing the noise from the feelers? My first instinct as a student would have been to push the stick forward - not good! Will they be trained to always do a go around?

 

Not Charlie Tango (or Anticept), but not sure a go around with the airplane firmly on the ground is the best option. The tail is pretty unlikely to hit with the mains still in the air*.

 

I would likely train them by pushing the tail down with them in it to get the sight picture when the feeler hits - which, if like the Cirrus, would be quite extreme. Then train them so that if they hear scraping, just relax a tiny bit of back pressure until it stops, then continue.

 

But That's Just Me™, with the caveat I've never landed a CT.

 

BTW, happy to do a photo session with Andy any time he wants an excuse to fly to Copperhill!

 

 

*Porpoising is another matter, and then the best bet if full throttle and just hold a reasonable climb attitude until clear of the ground and climbing.

[Roger Lee]

The problem with our CT underfin is it has no structural integrity and is there for flight characteristics. It was built very light and hollow for weight considerations. If you strike the tail on landing it may scrape it, but several have found out you can crush it. Then it has to come off and be completely stabilized inside and refinished outside. The tail skid does work for a light contact or if you push the tail down a little too hard and fast when moving it by hand.

[Ed Cesnalis]

Eddie,

 

If I was to contact my tail first wouldn't that reduce my AOA and cause my mains to contact?  I too would relax a little.

[Anticept]

Just as a side note, one should not beef up the tail strake structure, as this means all that energy is going to travel somewhere else. While I agree it's flimsy, it's also a great shock absorber considering. It also helps protect the stabilator from striking too if someone lands too hard and the tail bounces.

[Doug G.]

Yeah, I was thinking that a quick push with the mains down, if the plane is not at stall speed, could lead to lifting off slightly and a noise wheel strike, then proposing. Or am I mis-analyzing this?

[Anticept]

Porpoising takes a lot of force. Generally that happens when someone stalls just after ballooning and the plane drops from a few feet. That's what happened with one of the tail strikes we were talking about, the guy came in and botched the landing, hit the tail, dropped the nose, and instead of holding back, he kept trying to fight it by pushing forward and pulling back, making it worse. Bent up the nose wheel, and badly damaged the strake.